But considering a higher power as even a plausible hypothesis is purely due to historical reasons. Alien mind control, Illuminati mind control, living in a simulation, or humans being the fruiting body of Gaia would be impatiently dismissed despite requiring fewer assumptions than an all-powerful entity. Why should that idea even be entertained, rigorously speaking?

It's difficult to speak of rigor for any of these hypotheses, but anyways. If we take "higher power" to roughly mean that there is some driving force, whether personal or impersonal, that inherently defines and imposes order and fate, I can see how it is compelling. It's simpler than introducing a third party like aliens or the Illuminati, and early humans had much less reason to feel they weren't just another part of the natural ecosystem. They were struggling against natural forces, and when interesting and terrifying things happened, they thought of these as supernatural forces, not having developed theories of, say, lightning or disease.